1. Field of Invention
This invention relates to a filtering apparatus. More specifically, it is directed to an improved filtration system for extracting liquid from a sludge or slurry and separating the resulting liquids and solids for separate disposal or recovery.
Sludge includes any solid-liquid sludge and slurry such as sewage and industrial waste. The sludge may contain any ratio of liquids to solids. In fact, the sludge often has substantially more solid material than liquid material. Separation of the sludge into its liquid and solid components, also known as "dewatering," is desirable for recovery or disposal of the one or both of the components.
One typical manner of dewatering sludge involves placing the sludge into a container that has filters therein. The liquid in the sludge passes through the filters and from the container. However, the filters do not permit the solids to pass therethrough. Therefore, the solids remain in the container and are removed after the dewatering operation is complete.
Generally, the fluid is drawn through the filter in one of two ways, vacuum drainage or gravitational drainage. Vacuum drainage requires the use of a pump in flow communication with the filtrate cavity of the filter. In order to utilize a pump that can develop a vacuum, the filtrate cavity must remain below the liquid surface level at all times.
In addition, vacuum drainage often results in filter blockage. In this type of system, activation of the pump draws the sludge liquid as well as the sludge solids toward the filters. However, during the initial stages of dewatering when the liquid concentration is highest, the smaller sludge solid particles more readily flow toward the filter and tend to block the filter element. Blockage of the filter element hinders dewatering speed and efficiency.
Gravitational drainage does not require a vacuum and, therefore, does not require maintenance of the filtrate cavity below the sludge liquid surface. Consequently, the filters in such a system can extend the entire height of the container and, thereby, provide greater drainage surface area. Also, because gravitational drainage is slower than vacuum drainage, the sludge solid particles settle on the filter surface in a more uniform manner and provide an additional filtering layer. Thus, the filters do not experience blockage. However, as mentioned, gravitational drainage is relatively slow.
2. Related Art
The described sludge dewatering systems have long been known to the prior art. Illustrative of such systems are U.S. Pat. No. 392,607, U.S. Pat. No. 3,970552, German Pat. No. 3,604,616 Al, and U.S. Pat. No. 4,871,545.
Though the above referenced and described dewatering systems may be helpful in dewatering sludge, they can be improved to provide faster and more efficient sludge dewatering and filtration.